An antagonist to opioids. It can cause distress and some signs of withdrawal if injected by heroin users, a so-called naloxone challenge.

An opioid (opiate) drug, e.g. morphine or heroin.

Driving force of evolution as described by Darwin. In the competition for resources between individuals in an environment that cannot support all of a population, a natural process of ‘selection’ occurs in which individuals with the most adaptive characteristics are more likely to survive and reproduce.

This refers to debates about the relative contributions of genetic inheritance (nature) and environmental influences (nurture) to the physical/ behavioural characteristics of an organism or species.

Tendency to construe the world in negative terms; characteristic of a depressed mood.

(in cell metabolism) Also called end-product inhibition. It is the mechanism by which a metabolic pathway is regulated: when the product of the pathway exceeds a critical concentration, it ‘switches off’ an enzyme early in the pathway, thereby preventing further synthesis of the regulatory end-product.

A system in which a displacement of a variable from a state causes corrective action such as to return the variable to that state.

Another name for a neuron.

The collection of all of the neurons of the body, in brain, spinal cord and periphery.